This invention relates to an echo canceller operable as an echo cancelling device.
In a long-distance telephone network, a local telephone substation is connected through a hybrid transformer and a two-wire line to a plurality of remote telephone substations. An echo canceller is connected to the hybrid transformer between two wires of the two-wire line. A sent signal originates at the local telephone substation and is delivered through the hybrid transformer to the echo canceller and thence to the remote telephone substations. For reception at the local telephone substation, a received signal originates at one of the remote telephone substations and is delivered to the echo canceller and thence to the hybrid transformer.
It is usual in the art to refer to the sent signal as a send-in signal and a send-out signal while transmitted from the hybrid transformer to the echo canceller and from the echo canceller towards the remote telephone substations. The received signal is called a receive-in signal while transmitted from one of the two wires to an echo canceller.
As will later be described, a conventional echo cancelling device is not exempted from factors which deteriorate a quality of speech transmission either in a bidirectional communication state or when a channel noise or a background noise is high.